Effect of calendering speed on sheet structure and paper properties

The effect of calendering speed on the collapse of newsprint during calende ring has been investigated. Uncalendered 45 g/m(2) paper made on STFI's FEX experimental paper machine from Pinus radiata thermomechanical pulp (TMP) was calendered at 5, 22, and 100 m/min. Nip pressures were adjusted so that the resultant densities were comparable for the three calendering speeds. Cross-sectional macro-pore structure and other paper properties were invest igated. Both interfibre areas and lumen areas decreased about 20% with calendering, compared with a 28% reduction in apparent thickness and a 15% reduction in effective thickness. Calendering speed was found to have no significant effect on pore areas, no r did it significantly affect most paper properties. This suggests that low speed laboratory calenders should be able to be used to simulate the effec t of high speed commercial calendering on paper structure, Effective densit y was compared to apparent density as a value for describing the density of paper. Effective density values, which are calculated from the bending and tensile stiffnesses of paper, and are regarded to be closer to 'true' density than 'apparent' density values, were significantly higher than apparent density values, and showed a much smaller increase with calendering.